Disc drives that read and record digital information on a disc-shaped information storage medium are in wide-spread use. Such discs include compact discs (CDS), read-only-memory compact discs (CD-ROMs), rigid magnetic discs, and flexible magnetic discs. Rigid magnetic discs include both fixed discs and removable discs that are housed in cartridges. An example of a removable cartridge having a rigid disc assembly is the JAZ.TM. cartridge and an example of a removable cartridge having a flexible magnetic disc assembly is a ZIP.TM. cartridge, both of which are produced by the assignee of the present invention, Iomega Corporation, Roy, Utah.
FIG. 4 (prior art) illustrates a conventional rigid disc assembly 110a that includes hub assembly 112 and platter 114a. Hub assembly 112 includes a metallic hub 116a, clamp 118, and multiple rivets 120. Platter 114a is held between surfaces of the clamp 118 and hub 116, which are held together by rivets 120. Unfortunately, rivets 120 may cause distortion of platter 114a because of dimensional imperfection or dis-uniformity in producing or assembling the components. Even if the components are produced with tight manufacturing and assembly tolerances, platter distortion may still be a problem because of the sensitivity of the reading and recording process to even small amounts of distortion. Specifically, distortion of platter 114a as small as an order of magnitude of 1.0.times.10.sup.-6 inch may cause interruption of the reading and recording process. The industry trend toward increasing areal density of stored information will likely diminish the acceptable amount of distortion.
Furthermore, platter 114a may slip with respect to hub 116a upon shock to disc assembly 110. Such slip may cause the center of platter 114 to be misaligned with the center of spindle motor 122a, which leads to difficulty in track following by the heads. Although removable cartridges are naturally more prone to shocks that may cause such slip, fixed discs (not shown) may also be subject to such shock, especially during shipping and installation. Moreover, the tight tolerances and several steps required to produce hub assembly 112 result in high cost of discs. Users of information storage discs are sensitive to cost and the industry is cost competitive.
FIG. 5 (prior art) illustrates another conventional disc assembly 110b that includes a platter 114b and a hub 116b. Platter 114b is affixed to a mating surface 117 of hub 116b by an adhesive. Not only does using adhesive have the disadvantages of platter 110a discussed above, but using adhesives causes additional difficulty in the assembly process. For example, adhesives can out-gas and deposit back onto the discs in the drive and cause head stiction and flying height problems. Also imprecise or dis-uniform application of the adhesive may weaken the joint and the adhesive may inadvertently be spilled or splattered onto the information-bearing surface, which may interrupt reading and recording information, and may also damage the heads. The disadvantages of disc assemblies 110a and 110b described herein apply to both rigid and flexible discs, and to fixed and replaceable discs.
It is desirable to provide a disc assembly, and associated disc drive, that diminishes slipping of the platter if subject to shock, that holds the platter uniformly around its inner circumference to eliminate localized distortion near clamp rivets, and that is less costly and more easily produced without extraordinarily tight tolerances of the components.